Conventionally, spectroscopic detectors have been used for an analysis of a sample which enters a flow cell after being doted from a column in a liquid chromatograph (see Patent Literature 1).
FIG. 4A is a top view of a spectroscopic detector 90 described in Patent Literature 1, and FIG. 4B is a front view of the same detector. In this spectroscopic detector 90, as shown in FIG. 4A, polychromatic light is generated from a light source 91, which includes a xenon lamp. After being reflected by an excitation light mirror 921, this light passes through a slit 961 and falls onto the surface of an excitation light diffraction grating 931, which disperses the light into a spectrum. From among this spectrum of light, a specific wavelength of light passes through a slit 94 and enters the flow cell C as the excitation light. The sample in the cell C is irradiated with this excitation light and emits observation light. The rotatable excitation light diffraction grating 931 is rotatable. By turning this grating 931, the wavelength of the excitation light which is extracted from the polychromatic light of the light source 91 and introduced into the flow cell C, is changed according to the kind of sample to be analyzed.
As shown in FIG. 4B, the observation light generated from the sample is reflected by a mirror (not shown) placed within the flow cell C, to be extracted through the exit window W to the outside of the flow cell C. After being reflected by an observation light mirror 922, the light passes through a slit 962 and falls onto the surface of an observation light diffraction grating 932, which disperses the light into a spectrum. By turning the observation light diffraction grating 932, the amount of light at each wavelength within the spectrum can he detected with a photodetector 95. As the photodetector 95, for example, a photodiode array or photomultiplier tube is used. It should be noted that, for an easy view of the optical system, the observation light mirror 922 and the observation light diffraction grating 932 are omitted from FIG. 4A, while the excitation light mirror 921, the excitation light diffraction grating 931 and the slit 94 are omitted from FIG. 4B.